1. Field of the Invention
An aspect of the present invention relates to a supported catalyst for a fuel cell, a method of preparing the same, an electrode for a fuel cell including the supported catalyst, and a fuel cell including the electrode, and more particularly, to a supported catalyst for a fuel cell using a graphite based catalyst carrier to increase durability of the fuel cell, wherein the supported catalyst for the fuel cell achieves superior energy density and fuel efficiency by minimizing the loss of a metal catalyst impregnated in the graphite based catalyst carrier and by regulating the amount of the impregnated metal catalyst, a method of preparing the same, an electrode for a fuel cell including the supported catalyst, and a fuel cell including the electrode.
2. Description of the Related Art
Fuel cells can be classified into polymer electrolyte membrane fuel cells (PEMFCs), phosphoric acid fuel cells (PAFCs), molten carbonate fuel cells (MCFCs), solid oxide fuel cells (SOFCs), etc., according to the kind of electrolyte used in the fuel cells. The operating temperature of fuel cells and constituent materials of the fuel cells vary according to the type of electrolyte used.
According to the method of supplying fuel to the anode, fuel cells can be classified into an external reformer type where fuel is supplied to the anode after being converted into hydrogen-rich gas by an external reformer and an internal reformer type or direct fuel supply type where fuel in gaseous or liquid state is directly supplied to the anode.
A representative example of a direct fuel supply type fuel cell is a direct methanol fuel cell (DMFC). DMFCs use aqueous methanol solution as fuel, and a proton exchange polymer membrane with ionic conductivity as an electrolyte. DMFCs are small and lightweight but can achieve a high output density. In addition, an energy generating system having a simple structure can be manufactured using PEMFCs.
A basic structure of a PEMFC includes an anode (fuel electrode), a cathode (oxidant electrode), and a polymer electrolyte membrane disposed between the anode and the cathode. A catalyst layer for facilitating the oxidation of fuel is formed on the anode of the PEMFC, and a catalyst layer for facilitating the reduction of an oxidant is formed on the cathode of the PEMFC.
In the anode of the PEMFC, proton ions and electrons are generated as a result of the oxidation of fuel. The proton ions migrate to the cathode through the polymer electrolyte membrane, and the electrons migrate to an external circuit (load) through a wire (or a current collector). In the cathode of the PEMFC, the proton ions transmitted through the polymer electrolyte membrane and the electrons transmitted from the external circuit through a wire (or a current collector) combine with oxygen, thereby generating water. Here, the migration of electrons via the anode, external circuit, and cathode produces an electric current. As described, the cathode and/or the anode contain a catalyst which can accelerate electrochemical oxidation of fuel and/or electrochemical reduction of oxygen.
Conventionally, PEMFCs use platinum particles dispersed in an amorphous carbon carrier as catalysts for a cathode and an anode, whereas DMFCs use PtRu as a catalyst for an anode and platinum particles themselves or platinum particles dispersed in a carbon carrier as a catalyst for a cathode.
U.S. Pat. No. 6,306,543 and U.S. Pat. No. 6,551,960 disclose a method of preparing a supported catalyst wherein platinum particles are dispersed in a carbon carrier using a polyol process. FIG. 3 is a schematic flowchart illustrating a method of preparing a supported catalyst according to a conventional method. Referring to FIG. 3, the method of preparing a supported catalyst, wherein platinum is impregnated in a carbon based catalyst carrier, includes mixing a platinum precursor solution and a dispersed solution of a carbon carrier; titrating the pH of the mixture; heating and cooling the mixture; and filtrating, cleaning and drying the resultant mixture.
The conventional supported catalyst uses a graphite based catalyst carrier, which can easily withstand heat, to prevent the loss of platinum, as a catalyst metal, for an increase in the durability of a fuel cell. However, such a supported catalyst cannot contain a certain amount of the metal catalyst, for example, about 40 wt % or more.